This invention relates to control systems for driving stepping motors and more particularly to a dynamically variable loop filter drive control circuit for synchronizing a color filter wheel for a color video borescope.
The use of color video systems for viewing remote regions has become a powerful diagnostic tool in the industrial and medical fields. In U.S. Pat. No. 4,074,306, a color endoscope is disclosed wherein a filter wheel is employed to sequentially illuminate a target to provide color separated image information which is processed in the video system to present a color separated image of the target area one over the other upon a television screen. As can be seen, both a sharp image and a faithful reproduction of the original colors is important in making an accurate diagnosis and any loss of image registration or the like will adversely affect the results of the examination.
In U.S. Pat. No. 4,523,224 to Longacre, there is shown an open loop motor control unit for synchronizing the stepping rate of the motor to the field rate of the video system in response to the master clock signal so that the filters are brought past the fixed optical path in timed sequence with each of the video field periods.